Field of the Invention
The invention relates to a method and device for conveying single sheets or for conveying a shingled sheet stream in a feeder region of a sheet-processing machine by means of a conveyor table which is equipped with at least one endless conveyor belt, guided over at least two rotatably supported deflection rollers, the conveyor belt conveying the sheets in a region between a sheet pile and front stops, wherefrom the sheets are transferred to the sheet-processing machine.
The sheets are lifted from a sheet pile by a suction strip or a suction head and transported individually or in a shingled manner across a conveyor table into the sheet-processing machine. In the vicinity of the conveyor table, the sheets are aligned so that they are taken over in-register by the sheet-processing machine. Alignment of the leading edges of the sheets occurs at the front lays of the conveyor table.
Heretofore, the feeding of sheets to the sheet-processing machine took place in accordance with the operating cycle of the machine; it was heretofore customary to couple the conveyor belt of the conveyor table to the main drive of the sheet-processing machines. From the published Japanese Patent Document JP-PO 3-295651, it has become known heretofore to drive the suction conveyor belt via a separate motor. In particular, the leading edge of a sheet is ascertained by a leading-edge sensor and, thereafter, a control device adjusts the velocity of the motor so that mechanical errors, which occur when suction is applied to the sheets, are corrected, and so that the sheet transport is thus optimally adjusted to the processing velocity of the sheet-processing machine.
From Japanese Utility Model Sho 61-83924, a delay device for sheet-fed printing presses has become known heretofore. In this case too, the main drive of the printing press is used to drive the conveyor belts of the conveyor table, but superimposed on this drive, however, is a cyclical motion of the conveyor belts for conveying the sheets, which operate in accordance with the operating cycle of the sheet-processing machine. By using a gear transmission with a plurality of eccentric gear wheels, the velocity of the conveyor belt is sinusoidally modulated in accordance with the machine operating cycle.
The gear transmission coupled to the main drive and having eccentric gear wheels has several disadvantages. First, the construction thereof dictates a fixed velocity profile. The velocity profile also exhibits only one maximum and one minimum, and the maximum and minimum can be reached at precisely one point. Furthermore, in the region of the feeder, a suitably ample amount of construction space for the gear transmission must be created. Last but not least, the individual parts of a mechanical transmission are subjected to major wear.